Mud motors are powerful generators used in drilling operations to turn a drill bit, generate electricity, and the like. The speed and torque produced by a mud motor is affected by the design of the mud motor and the flow of mud (drilling fluid) into the mud motor. Control over these parameters is attempted from the surface of a wellbore by adjusting the flow rate and pressure of mud, adjusting the weight on the drill bit (WOB). The fidelity of control by these techniques is poor, however. Motors can stall and suffer speed variations as a consequence of loading and drill string motion. Accordingly, there is a need for devices and methods for more responsively and precisely controlling the operation of a mud motor.